In many situations, there is a need for protective layers which can be integrated into various body-protecting products in order to prevent injuries caused by penetrating objects such as nails, pointed weapons and the like. One area where a great need exists for protection against penetrating nails is footwear for people who work on construction sites, where inter alia construction timber with projecting nails is found. Treading on a nail can give rise to serious foot injuries and infections.
It has long been known to use inserts made of steel or metal in footwear for construction workers. Such metal inserts can provide good protection but have certain disadvantages. Among other things, they contribute to making the shoe relatively rigid and stiff. This prevents normal bending of the foot and impairs the sense of feeling against the ground, which can increase the risk of inter alia falling and slipping accidents.
In order to overcome some of these problems, U.S. Pat. No. 1,701,611 describes footwear with a flexible metal insert which comprises a woven metal wire fabric. However, the use of metal also results in other disadvantages, as metals are usually good conductors of both heat and electricity. Shoes with metal inserts therefore impair the possibility of keeping the foot warm in a cold climate and can, on account of their conductive capacity, constitute risks in some workplaces and for certain occupational groups such as, for example, electricians.
In order to eliminate problems associated with using metal, the use of synthetic fiber material embedded in a shoe sole has previously been proposed. In this connection, the fibers are woven into a fabric, and one or more layers of such a fabric can then be molded integrally in a shoe sole, so that the material of the shoe sole completely impregnates the woven layers. An example of a protective boot with such a sole is described in U.S. Pat. No. 5,979,081.
WO 99/13744 describes a variant of a protective boot with layers of synthetic fiber fabric integrated into the sole. In this case, the fibrous fabric is not impregnated with binder in the sole but can, for example, be fitted in a pocket formed between the inner and the outer sole of footwear.
It is common to all known protective layers using synthetic fibers with high ultimate strength that the fibers are applied in the form of a woven fabric or the like, that is to say in a structure in which the fibers are in some way arranged in a predetermined pattern relative to one another. Testing has nevertheless shown that a nail, for example, is capable of “finding its way through” any arranged fibrous structure, even if the latter consists of a very tight weave. In order to prevent this, an impractical number and thickness of woven layers would be required. This would make the shoe clumsy, and increase its weight and the consumption of expensive fibrous material.